Top Gun DR650 Secondary
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|DR-650 Secondary Air Filter
|Notice the much smaller area for
air intake on the stock filter
|A Top Gun filter shown in the
proper position for seat
As mentioned in the January 07 "Technical Insights" and in Elden's February , March,
and April "Fuel For Thought" articles, we've found a potential problem - and solution -
of which most riders may not be aware. We can't blame you since it's not even
addressed in the factory service manual.
The secondary air filter lives under your seat. It consists of a piece of foam (which
appears to be pretreated by the factory with oil) in a plastic housing, and it's
construction is not conducive to regular cleaning. As mentioned already, the filter is
absent from the periodic maintenance section of the service manual. Why then, you
might ask, should I be worried about it?
Your constant velocity carburetor relies on a diaphram/slide combination to correctly
meter fuel. This diaphragm works by moving up and down in response to varying
engine demand. The secondary air filter is meant to keep dirt and debris from entering
an air hose that supplies air to the carb that helps modulate the slide. Any dirt or debris
that might enter could hinder diaphram/slide movement which in turn reduces your
carb's ability to respond rapidly to changing engine demands.
What are the advantages of the Top Gun filter?
For best throttle response, the diaphram/slide should move as freely as possible. The
Top Gun filter does this by providing a much larger surface area for air passage,
combined with a filter construction that makes it easy to remove and service. Notice in
the top-left picture above how small the opening to the stock air filter is compared to the
available surface area of the Top Gun filter.
The Top Gun filter element is made of foam so it can be cleaned and oiled with any
quality foam filter products. We recommend UNI since they carry a convenient spray-on
type oil and cleaner specially formulated for foam filters.
Although the service manual doesn't specify a maintenance interval, we recommend
inspecting your secondary air filter every 2,000 miles (same interval as your primary air
filter). As we do with our primary air filters, we recommend purchasing two filters. One
filter can be installed leaving lots of time to clean the old one. Store your newly-cleaned
filter in a ziploc bag and it's ready to go - just oil and install!
Note - If you have a lot of miles, especially in the dirt, on your DR and have never
serviced your stock secondary air filter, we recommend inspecting your carburetor prior
to installing the Top Gun filter. Installing our filter won't fix a sticky slide due to
pre-existing dirt. Click here to see what happens when your filter isn't working.
Since the Top Gun filter isn't encased in
hard plastic, a few easy steps should be
followed to avoid any damage when
reinstalling the seat. Position the filter as
close to the left frame member and airbox
inlet tube as possible (see picture
top-right). You can adjust the black
factory hose-routing clamp to properly
position the filter. For additional
clearance, we recommend removing some
material from the seat tang (see photo
right). The filter will fit without this removal,
but even shaving 1/4" makes reinstalling
your seat a breeze.
|Seat tang slightly modified to
provide additional filter clearance.